The present invention relates to a long nip press roll, particularly for use in machines for the manufacture of paper, cardboard, or the like, and, in particular, for removing water from a traveling paper web, and particularly to features of the press shell and press shoe which control the travel of the fiber web around the press shell.
The starting point of the invention is a long nip press roll in accordance with U.S. Pat. No. 4,555,305, incorporated herein by reference, or U.S. Pat. No. 4,673,461. The invention is preferably used in the first of these long nip press rolls. In that press roll, the two ends of the tubular press shell are fastened directly to support disks which are arranged coaxially with the press shell. For details, see U.S. Pat. No. 4,625,376, incorporated herein by reference. If the path of rotation of the press shell is to be eccentric with respect to the longitudinal axis of the support body, then, in accordance with German Patent Application No. P 37 08 189.6, which corresponds to U.S. application Ser. No. 164,542, filed Mar. 7, 1988, the two support disks are mounted in the same way eccentrically on the support body or support beam. Because of the direct attachment of the ends of the press shell to the two support disks, compressed air can be fed to the inside of the press shell so that its inside is continuously under a certain positive pressure. Furthermore, by means of springs, namely springs 21 in FIG. 1 of U.S. Pat. No. 4,625,376, which act upon the support disks, along the axial direction of the roll, the press shell can be placed under a certain axial stress between the disks. These measures cause the press shell to revolve quietly outside the elongate press nip on its substantially circular path, without mechanical support or guidance elements for guidance of the press shell being necessary outside the press nip.
Known long nip press rolls of this type have been used up to now predominantly for removing water from relatively thick paper webs. The paper web travels as a rule through the lengthened press nip between two felt belts. In that case, the press shell preferably has a relatively rough outer surface which contacts one of the felt belts. The present invention is concerned with the problem of permitting operation with only one felt belt, wherein the web of paper travels through the press nip between the felt belt and the press shell. This is in contrast to other known single felt arrangements in which the paper web travels through the press nip between the felt belt and the backing roll.
East German Patent No. 79,919 and U.S. Pat. No. 4,201,624 disclose long nip presses of a different type, in which the web of paper travels through the elongate press nip between a felt belt and an elastic press belt which travels around rolls. Those patents, however, disregard the difficulty, which is experienced particularly with relatively thin types of paper, of separating the paper web cleanly, i.e. as uniformly as possible over the width of the web, following its outlet from the press nip from the elastic press belt and at the same time of seeing that the danger of rewetting, i.e. flowing back of water from the felt belt into the paper web, is kept as slight as possible.